This invention relates to an apparatus for applying photo-etching on one surface of a semiconductor wafer formed with oxide film thereon.
In manufacture of semiconductor circuits, oxide film is formed on surfaces of a semiconductor wafer made of silicon, and then photo-etching of oxide film on one surface of wafer is carried out in order to permeate diffusion material of either P-type or N-type selectively on said one surface. Therefore, photosensitive liquid (photo-hardening type photoresist) is coated in a thin film form on predetermined portions of the wafer surface, and next printed thereon and developed for forming a pattern for photo-etching of oxide film, said pattern providing a semiconductor circuit, while the other surface of wafer is not formed with any pattern so that oxide film thereon is wholly exposed.
However, in a commonly accepted technique, the oxide film etching is carried out in a carrier for etching in which a suitable number of wafers are received, and wafers in the carrier are dipped into an etching liquid in a dipping container. Accordingly, oxide film of the wafer surface under portions of the pattern of photoresist remains without any effects of etching, while oxide film of other portions of wafer surfaces, i.e., the main and rear surfaces of wafer, is removed by etching, which provides exposure of silicon on the removed portions. Then, after removal of the photoresist, the wafer is treated with diffusive permeation of P-type or N-type diffusion material within a diffusion oven of a high temperature such as 800.degree. C.-1200.degree. C. In the diffusion process, the rear surface of a wafer having no oxide film is permeated with diffusion material in the same way as the main surface. Such a wafer of which the rear surface is permeated with diffusion material can not be used as it stands, due to its characteristics. Therefore, it is required to delete the permeated depth portion of the rear surface by grinding or the like. Also, there is selectively remaining oxide film on the main wafer surface, but there is no oxide film on the rear wafer surface, so that the wafer suffers deflection and/or torsion due to difference in thermal expansion rate between the main and rear surfaces of wafer in the process within the diffusion oven, which may provide a serious defect on the wafer. Further, in the oxide film etching process of the dipping type, it is difficult to remove any reaction gas caused in the process, said gas being apt to contact to wafer surfaces, so that it may result in unevenness in etching reaction.
Therefore, an object of the present invention is to provide an apparatus for applying photo-etching on one surface of a semiconductor wafer, in which only one surface of a wafer is contacted with etching liquid to thereby hold oxide film of the rear surface as it stands, so as to obviate deletion of a permeated depth portion of the rear wafer surface as well as to prevent any deflection and torsion of the wafer in the diffusion process.
Another object of the invention is to provide an improved apparatus for etching of oxide film of semiconductor wafer in which the wafer surface is not contacted with any reaction gas caused in the etching process.
In attaining the described objects of the invention, an etching apparatus according to the present invention includes a cup-shaped basin having at the bottom thereof a vertical passage for introducing etching liquid, a chuck rotatably supported above said basin for vacuum-absorbing a semiconductor wafer at the bottom surface thereof and support means for supporting the wafer temporarily and horizontally before the wafer is vacuum-absorbed by the chuck. Said one surface (main surface) of a wafer is downward facing and is contacted with etching liquid that is blown vertically upward through the vertical passage of the basin, to thereby prevent the upward facing rear surface of a wafer from being contacted with etching liquid. This etching apparatus also includes means for rotating the chuck so as to remove any reaction gas resulted on the one surface of a wafer by centrifugal force.
The invention and its objects and advantages will become more apparent in the following detailed description of the preferred embodiments of the invention.